Implantable medical devices typically comprise a case that is generally referred to as a “generator,” electrically and mechanically connected to one or more “leads” that are in turn provided with electrodes intended to come in contact with the tissues to be stimulated by delivering an impulse (or pulse) and/or detected by sensing (or collecting) an electric signal: myocardium, nerve, muscle . . . etc. In the case of an implantable medical device for therapy, these electrodes can be intracardiac electrodes (placed in a cavity of the myocardium in contact with the intra-cardiac wall), pericardial (in particular, to define a reference potential, or to apply a shock), or intravascular (the lead, for example, is introduced into the coronary sinus until a site located in front of the wall of the left ventricle).
A first aspect of the development of applications for these devices is the multiplication of the number of electrodes, in particular for the devices known as “multi-site” which make it possible to choose the sites of stimulation/detection in order to optimize the functioning of the device. Thus, in the particular case of the devices for the ventricular re-synchronization (such devices being known as Cardiac Resynchronization Therapy or “CRT” devices), once implanted into the patient a device provided with electrodes allowing to stimulate both ventricles. The stimulation of the right ventricle (and the right atrium) is operated by a traditional intracardiac lead, but for the left ventricle the access is more complex: the stimulation is generally operated by means of a lead introduced into the coronary sinus of the right ventricle and then pushed in a coronary vein on the pericardium, so that the extremity of the lead comes to be placed in front of the left ventricle. This procedure is rather delicate, because the diameter of the coronary vessel is reduced as the lead advances, so that it is not always easy to find the optimal position at the time of the implantation. Moreover, the proximity of the phrenic nerve can sometimes lead to inappropriate stimulations. It is to overcome these difficulties that the development was conducted on leads to obtain what is known as a “multi-electrode” lead, provided with, as an example, ten electrodes and of which it is possible to select after implantation the most effective stimulation electrode.
To manage this multiplicity of electrodes, multiplexing systems were developed allowing the connection of the various electrodes with the two wires traversing the lead and connected at the output of the generator. The U.S. Patent Publication 2003/0149456 A1 (Rottenberg et al.) described a generator connected to a multi-electrode lead by two wires associated with a multiplexer/demultiplexer. These two wires, on the one hand, ensure the sensing of the depolarization signals and the delivery of the stimulation impulses, and, on the other hand, deliver to the multiplexer/demultiplexer the logical signals making it possible to control selection switches for one or more electrodes on the lead. These signals also ensure the supply to the multiplexing/demultiplexing circuit and to the switches the necessary energy for their functioning. The multiplexing/demultiplexing circuits and the switches are preferably located at the extremity of lead, therefore remotely from the generator.
Another aspect of the use of the implantable device is the integration of various sensors within the lead, more particularly of a blood acceleration sensor or a blood pressure sensor, in particular a sensor of the endocardiac acceleration (EA). The signals collected by these sensors allow the control of various functions of the device: in particular, the measurement of the peaks of endocardiac acceleration (PEA) gives representative information of the instantaneous hemodynamic state of the patient.
Documents EP 0515319 A1 and its counterpart U.S. Pat. No. 5,304,208, EP 0582162 A1 and its counterpart U.S. Pat. No. 5,454,838, and EP 0655260 and its counterparts U.S. Pat. No. 5,693,075 and U.S. Pat. No. 5,496,351 (all three in the name of Sorin Biomedica Cardio SpA) describe endocardiac acceleration sensors provided at the distal end of an intracardiac lead, introduced into the myocardium and connected to the pacemaker or a defibrillator case.
The presence of such sensors at the distal extremity of lead requires a specific connection for the transmission of the signals from the sensor to the generator connected at the opposed proximal extremity. This specific connection to the sensor comes in addition to the already existing connections between the generator and the electrodes located at the distal extremity of lead, connections themselves ensured by specific wires, with or without multiplexing.
Lastly, a third aspect of the recent development of the implantable medical devices, in particular in the cardiac field, is the multiplication of the number of leads connected to the same generator. More recently developed devices typically include three different leads, respectively associated with the right ventricle, the left ventricle and the right atrium, each one of these leads itself being provided with several electrodes, and eventually with a sensor at the distal extremity of lead.
The document WO 2006/029090 A2 (Proteus Biomedical, Inc.) proposes a system in which one two-wire bus conveys digital signals of selection/configuration of satellites integrated into the lead, as well as pulses of stimulation and analog sensed signals of the patient. Concern with this system arises with the fact that the coded selection/configuration signals also are delivered to the heart via the electrodes of the lead in the form of salvos of impulses. It is therefore necessary to very carefully calibrate these impulses in order not to start an inappropriate depolarization of cardiac tissue.